1. Field of the Invention
The present invention relates to a compact printer, and more particularly to a compact printer having a printing drum in which a hammer mechanism is accommodated.
2. Description of the Prior Art
Various types of known printers utilizing a printing drum are classified into those having the hammer mechanism outside the printing drum and those having the hammer mechanism inside the printing.
In the printers utilizing external hammer mechanism, there is already known a so-called flying hammer printer in which a plurality of hammers, positioned to face the printing drum across a recording sheet, are selectively driven by corresponding electromagnets thereby hitting the types in the printing position on the printing wheel through the recording sheet to obtain a print thereon. Also, there is a printer of so-called printing drum selection method in which a platen positioned to face the printing drum across a recording sheet presses the sheet against the printing drum after desired types are aligned by the selective function of a printing drum selecting mechanism which is positioned behind the printing drum, to obtain the desired print.
These known printers are not compact printers because a relatively large space is occupied by the hammer driving mechanism or printing drum selecting mechanism.
Also, the aforementioned flying hammer type printer is associated with a high level noise because the hammers hit the printing drum through the recording sheet. Further, it requires a complicated mechanism for synchronizing the typefont with the hammers as printing occurs by instantaneous impact while the printing drum is rotated, eventually and nonsynchronization occurs leading to errors in printing.
On the other hand the printer of the printing drum selecting system requires a selecting mechanism for each digit of a character to be printed, thus leading to an increased number of component parts which associated with a complicated mechanism, renders it quite difficult to reduce cost.